The present invention relates to a gear wheel change transmission and, more particularly, to a motor vehicle gear wheel countershaft construction transmission comprising an input shaft, a main shaft coaxial to the input shaft and having a retarder brake with a drive shaft situated centrically to a braking rotation axis, in a driving connection with the main shaft via a power take-off with a planetary gear, with one central wheel of the planetary gear of the power take-off being connected with the non-rotating housing, another central wheel being connected with the drive shaft of the retarder brake, and the planet carrier being in driving connection with the main shaft.
In a gear wheel change transmission of the type shown in German Patent DE 38 37 142 A1, the braking axis of rotation of the retarder brake and the central axis of the planetary gear of the power take-off are arranged coaxially with respect to the countershaft of a single-range transmission. The planet carrier is driven via a gear wheel position as a component of the power take-off by the main shaft which is in parallel to the countershaft and is the output shaft of the gear wheel change transmission. The power take-off with the output-side gear wheel of its gear wheel position, the planetary gear of the power take-off as well as the retarder brake for which a hydrodynamic brake or retarder is used are housed in a special stator housing which is provided on the output-side lower housing end area of the transmission housing of the gear wheel change transmission. As a result, the required free moving space is limited when the gear wheel change transmission is used for driving an eight wheeler and the possibility is eliminated of mounting retarder-independent power take-offs in the rear on the transmission housing.
These disadvantages exist also in the case of a known gear wheel change transmission of the type shown in German Patent DE 35 36 928 A1 which has a planet wheel range-change transmission as a multirange transmission. The inner planet wheel is connected with the input shaft and the planet carrier is connected with the output shaft of the gear wheel change transmission. The outer planet wheel via a change-over device can be fixed in a non-rotatable manner either with respect to the output shaft or with respect to the transmission housing. The braking rotation axis of the retarder brake with the pertaining coaxial drive shaft are arranged parallel to the output shaft and are accommodated in a special housing which is joined to the rearward lower housing end portion of the transmission housing of the gear wheel change transmission. In the case of this known gear wheel change transmission, the power take-off for the retarder brake does not have a planetary gear.
In the gear wheel change transmission shown in British Patent GB-A 21 09 488 for a motor vehicle having a primary retarder which can be used as a retarder brake, a transfer case is arranged in the power flux between a driving engine and a main transmission. The transfer case comprises a two-speed planetary gear and a hydrodynamic primary retarder. The constructional arrangement is such that the output shaft of the driving engine and the main axis of rotation of the planetary gear as well as the braking axis of rotation of the primary retarder are each situated coaxially with respect to the input shaft of the main transmission. The planetary carrier is non-rotatably connected with the central output shaft of the transfer case and is connected with the output shaft of the driving engine by a drive-through clutch which can be engaged and disengaged. The outer central wheel of the planetary gear is connected with the output shaft of the driving engine by a gear clutch which can be engaged and disengaged, and can be braked by a gear brake which can be engaged and disengaged. The inner central wheel is non-rotatably connected with a hollow shaft which, penetrated by the output shaft of the transfer case, is connected with a gear brake which can be engaged and disengaged as well as with the rotor of the primary retarder.
The primary retarder has a two functions. First, in the start-up phase from the stopped condition of the vehicle, only the gear clutch is engaged which connects the central wheel with the output shaft of the driving engine so that the primary retarder operates in a rotating direction opposite to the rotating direction of the output shaft of the driving engine as a retarder brake on the inner central wheel, which is used as a transmission reaction. Second, in the coasting operation of the motor vehicle, the outer central wheel can be separated by the disengagement of its gear clutch from the driving engine and can be braked by the engagement of its gear brake. In this retarder braking operation, the rotor is geared up by the planetary gear from the direction of the main transmission, specifically in a rotating direction which is the same as the rotating direction of the output shaft of the driving engine. It is a disadvantage that the rotational speed of the rotor is a function of the engaged gear of the main transmission and that greater efficiency of the rotor is bad for the retarder operation because the blading must also be designed for the braking effect in the opposite direction when it is used as a retarder brake in the start-up phase.
German Patent DE 41 40 979 A1 describes a known vehicle driving device of a different type which is provided with a hydrostatic-mechanical torque division transmission between the driving engine and the axle transmission line, with an at least four-shaft planetary differential comprising at least two rows of planet gears, two sun gears, a web and a ring gear. Also, two main shafts form the input and the output and are respectively connected to different shafts of the planetary differential, and at least two hydrostatic machines are each, in at least one operating range, connected to a separate shaft of the planetary differential and operate alternately as a pump or as a motor. At least one of the hydrostatic machines, while the other hydrostatic machine is at least approximately stopped, during the transition from one into the other operating range, can be switched over via at least one shiftable clutch from the output-side main shaft to the non-drive-side sun gear and changed in the drive operation from the motor function to the pump function.
It is stated that this known driving arrangement is to be different from a conventional hydrodynamic primary retarder which weighs approximately 40 kg and requires additional installation space, particularly in the longitudinal direction. A relatively low rotational speed of a magnitude of up to approximately 2,000 rpm. would then be available for the drive of the retarder; in addition, such a primary retarder is comparatively expensive. In the known driving device, it was therefore attempted to provide a retarder which avoids the disadvantages of a retarder of conventional construction and arrangement. For this purpose, the rotor of a hydrodynamic retarder was connected to the shaft of the non-drive-side sun gear or connected by a clutch. This approach was supposed to be based on the knowledge that a significantly higher rotational speed is supposed to be available on the shaft of the non-drive-side sun gear of the torque division transmission than on the input or output shaft of the torque division transmission. It is stated that this retarder can be installed directly in the housing of the torque division transmission or physically in front between it and the internal-combustion engine.
An object of the present invention consists essentially in providing a multirange transmission comprising a retarder brake, in which the retarder brake is geared up regardless of the gear speed as well as with respect to the rotational speed of the output shaft and, because of its arrangement, does not interfere with the use of braking-independent power take-offs.
This object has been achieved according to the present invention by providing that the braking rotation axis is coaxial with respect to a rotation axis of the main shaft and the retarder brake, which together with the planetary gearset of the power take-off, is operatively arranged between a basic transmission comprising the input shaft as a transmission input, at least one countershaft and the main shaft as a transmission output on one side and an auxiliary transmission of planet wheel construction on the other side. The auxiliary transmission is situated in a transmission power flux in series between the main shaft and a coaxially arranged output shaft. A non-rotatable driving connection is provided between the planet carrier of the planetary gearset of the power take-off and the planet carrier of the auxiliary transmission, and a hollow shaft penetrated by the main shaft constitutes a connection between a central wheel of the planetary gearset of the power take-off and the retarder brake.
In the gear wheel change transmission according to the present invention, a secondary retarder is arranged between the planet carrier of the auxiliary transmission and the main shaft of the basic transmission, and is geared up by way of a planetary train. The secondary retarder can be arranged in a housing center portion of the transmission housing which also accommodates the basic transmission. The power take-off for this secondary retarder takes place via a planetary train which is driven at the rotational drive shaft speed by the planet carrier of the auxiliary transmission which is connected with the output shaft. The rotor of the secondary retarder can be connected with the outer central wheel of the planetary gearset of the power take-off. The stator of the secondary retarder and the inner central wheel of the planetary gear are connected with one another and fixed to the housing. Thus, a gear ratio of i=1+ (number of teeth of the inner central wheel)/(number of teeth of the outer central wheel) is obtained. In one currently preferred embodiment, a geared up gear ratio of i.congruent.1.4 can be implemented. However, another arrangement may also be implemented in that the outer central wheel is arranged to be fixed to the housing and the rotor of the secondary retarder is connected with the inner central wheel. The gear ratio will now be i=1+ (number of teeth of the outer central wheel)/(number of teeth of the inner central wheel). In another embodiment, a geared-up gear ratio of i.congruent.3.5 can be achieved.
The charging of oil to the secondary retarder may take place by oil from the lubricating oil circulating system of the gear wheel change transmission via ducts of the center portion of the housing.
Furthermore, in the gear wheel change transmission according to the present invention, a compact construction and sufficient free moving space for all power take-offs and eight wheelers is achieved, with the compact construction also resulting in a weight advantage. Naturally, because of its drive from the direction of the output shaft, the braking torque of the secondary retarder is independent of the engaged gear speed. It is also possible to operate the retarder brake without any driving-up.